Planetary gear speed reduction device and driving mechanism

CROSS REFERENCE TO RELATED APPLICATION

The present invention claims priority under 35 U.S.C. § 119 to Japanese Application No. 2015-213891 filed Oct. 30, 2015, and Japanese Application No. 2015-213892, filed Oct. 30, 2015, the entire contents of which are incorporated herein by reference, and priority is also claims to U.S. Provisional Application No. 62/202,418, filed Aug. 7, 2015, the disclosure of which is also incorporated by reference.

FIELD OF TECHNOLOGY

At least an embodiment of the present invention relates to a magnetic planetary gear speed reduction device. Also, at least an embodiment of the present invention relates to a driving mechanism equipped with the said planetary gear speed reduction device.

BACKGROUND

A magnetic planetary gear speed reduction device is conventionally known (Patent Reference 1, for example). A planetary gear speed reduction device disclosed in Patent Reference 1 is equipped with a sun gear which is a magnetic gear and four planetary gears which are also magnetic gears. The sun gear and the planetary gears are formed cylindrically; the four planetary gears are arranged to surround the sun gear from the outer circumferential side. On the outer circumference side of the four planetary gears, a cylindrical housing yoke is arranged. In this planetary gear speed reduction device, the outside diameter of the sun gear is smaller than the outside diameter of the planetary gears.

Further, in the planetary gear speed reduction device disclosed in Patent Reference 1, the sun gear is secured on the outer circumferential surface of an input shaft and also secured to the outer circumferential surface of rotary shafts. The rotary shafts to which the planetary gears are secured are rotatably held by a planetary carrier.

PATENT REFERENCE

<ul id="ul0001" list-style="none"><li id="ul0001-0001" num="0005">[Patent Reference 1] Unexamined Japanese Patent Application 2012-163186 Publication</li></ul>

In the planetary gear speed reduction device disclosed in Patent Reference 1, the outside diameter of the sun gear is smaller than the outside diameter of the planetary gears, and the distance between the planetary gears which are arranged adjacent to each other around the outer circumference of the sun gear is short. Therefore, in this planetary gear speed reduction device, magnetic interference may occur between the planetary gears which are arranged adjacent to each other, degrading the efficiency in transmitting the power force from the sun gear to the planetary gears.

Also, in the planetary gear speed reduction device disclosed in Patent Reference 1, friction loss in the planetary gear speed reduction device in the axial direction of the rotary shaft on which the planetary gears are fixed (that is, the axial direction of the input shaft to which the sun gears are fixed) is small.

Then, at least an embodiment of the present invention provides a magnetic planetary gear speed reduction device having a magnetic sun gear and magnetic planetary gears, and provides an planetary gear speed reduction device in which the efficiency of transmitting the power force between the magnetic sun gear and the magnetic planetary gears can be increased. Also, at least an embodiment of the present invention provides a driving mechanism equipped with the said planetary gear speed reduction device.

At least an embodiment of the present invention provides a magnetic planetary gear speed reduction device having a magnetic sun gear and magnetic planetary gears, and provides a planetary gear speed reduction device in which friction loss in the axial direction of a rotary shaft, to which the magnetic planetary gears are fixed, can be reduced. Also, at least an embodiment of the present invention provides a driving mechanism having the said planetary gear speed reduction device.

To achieve the above, the planetary gear speed reduction device of at least an embodiment of the present invention comprises a magnetic sun gear, multiple planetary gears which revolve around the magnetic sun gear while rotating on the axes thereof, and a magnetic internal gear arranged, surrounding the multiple magnetic planetary gears from the outer circumferential side; the outside diameter of the magnetic sun gear and the outside diameter of the magnetic planetary gears are equal to one another.

In the planetary gear speed reduction device of at least an embodiment of the present invention, the outside diameter of the magnetic sun gear and the outside diameter of the magnetic planetary gear are equal to each other. Therefore, in this embodiment, the magnetic planetary gears which are adjacent to each other on the outside circumferential side of the magnetic sun gear can be more distanced, thus making it possible to prevent magnetic interference between the adjacently-arranged magnetic planetary gears. Therefore, in this embodiment, the efficiency of transmitting the power force between the magnetic sun gear and the magnetic planetary gears can be increased.

In at least an embodiment of the present invention, the planetary gear speed reduction device is provided with a single magnetic sun gear and four magnetic planetary gears which are arranged at a pitch of 90 degrees around the magnetic sun gear. In this configuration, the magnetic sun gear and the magnetic planetary gears may be formed in the same shape and that the number of magnetic poles on the outer circumferential surface of the magnetic sun gear and the number of magnetic poles on the outer circumferential surface of [each] magnetic planetary gear are equal to each other. Also, the reduction rate of the planetary gear speed reduction device may be one-fourth. By configuring the planetary gear speed reduction device in this way, the magnetic sun gear and the magnetic planetary gears can be in a common use, making it possible to reduce the number of different kinds of components that configure the planetary gear speed reduction device.

The planetary gear speed reduction device of at least an embodiment of the present invention can be used in a driving mechanism equipped with a motor, which is connected on the input side of the planetary gear speed reduction device and connected also to the magnetic sun gear by an output shaft thereof, and a driving mechanism equipped with a reduction gear which is connected to the output side of the planetary gear speed reduction device. In this driving mechanism, the output shaft of the motor is connected to the magnetic sun gear of the planetary gear speed reduction device; since the magnetic planetary gear speed reduction device is arranged at a position at which the rotation speed is relatively fast, the noise of the driving mechanism can be reduced.

To achieve the above, the planetary gear speed reduction device of at least an embodiment of the present invention comprises a magnetic sun gear, multiple magnetic planetary gears which revolve around the magnetic sun gear while rotating on the axes thereof, a magnetic internal gear arranged surrounding the multiple magnetic planetary gears from the outer circumferential side, multiple rotary shafts, to which the multiple magnetic planetary gears are respectively secured, a planetary carrier for rotatably holding the multiple rotary shafts, and a main body portion which rotatably holds the planetary carrier and to which the magnetic internal gear is secured; the multiple rotary shafts are held by the planetary carrier such that they can move in the axial direction thereof with respect to the planetary carrier; the planetary carrier is held by the main body portion such that it can move in the axial direction with respect to the main body portion; when one of the multiple rotary shafts is set as a primary rotary shaft and the remaining rotary shafts, the primary rotary shaft excluded, are set as secondary rotary shafts, the total length of a gap in the axial direction between the primary rotary shaft and the planetary carrier on one end in the axial direction and a gap in the axial direction between the primary rotary shaft and the planetary carrier on the other end in the axial direction is smaller than the total length of a gap in the axial direction between the secondary rotary shafts and the planetary carrier on one end in the axial direction and a gap in the axial direction between the secondary rotary shafts and the planetary carrier on the other end in the axial direction, and the total length of a gap in the axial direction between the planetary carrier and the main body portion on one end in the axial direction; when the primary rotary shaft and the planetary carrier are in contact in the axial direction, a gap is to be created in the axial direction between the secondary rotary shafts and the planetary carrier and between the planetary carrier and the main body portion on both ends in the axial direction.

In at least an embodiment of the present invention, the magnetic center in the axial direction of the magnetic sun gear and the magnetic internal gear coincides in the axial direction with the magnetic center in the axial direction of the magnetic planetary gear; the external force in the axial direction exerted on the planetary carrier is less than the magnetic attraction in the axial direction working between the magnetic sun gear, the magnetic internal gear and the magnetic planetary gear fixed to the primary rotary shaft.

In the planetary gear speed reduction device of at least an embodiment of the present invention, the total length of the gap in the axial direction between the primary rotary shaft and the planetary carrier on one end in the axial direction and the gap in the axial direction between the primary rotary shaft and the planetary carrier on the other end in the axial direction is smaller than the total length of the gap in the axial direction between the secondary rotary shafts and the planetary carrier on one end in the axial direction and the gap in the axial direction between the secondary rotary shafts and the planetary carrier on the other end side in the axial direction, and the total length of the gap in the axial direction between the planetary carrier and the main body portion on one end in the axial direction and the gap in the axial direction between the planetary carrier and the main body portion on the other end in the axial direction. Also, in at least an embodiment of the present invention, when the primary rotary shaft and the planetary carrier are in contact in the axial direction, a gap is to be created between the secondary rotary shafts and the planetary carrier on both ends in the axial direction. Therefore, in at least an embodiment of the present invention, if the magnetic center in the axial direction of the magnetic sun gear and the magnetic internal gear coincides with the magnetic center in the axial direction of the magnetic planetary gears, even when friction loss occurs between one rotary shaft (the primary rotary shaft) and the planetary carrier, no friction loss in the axial direction will occur between the remaining rotary shafts and the planetary carrier. Therefore, in at least an embodiment of the present invention, friction loss in the planetary gear speed reduction device in the axial direction of the rotary shafts can be reduced.

In at least an embodiment of the present invention, when the primary rotary shaft and the planetary carrier are in contact in the axial direction, a gap is to be created in the axial direction between the planetary carrier and the main body portion on both ends in the axial direction. Therefore, in at least an embodiment of the present invention, when the magnetic center in the axial direction of the magnetic sun gear and the magnetic internal gear coincides with the magnetic center in the axial direction of the magnetic planetary gears and the external force in the axial direction exerted on the planetary carrier is less than the magnetic attraction in the axial direction working between the magnetic sun gear, the magnetic internal gear and the magnetic planetary gear which is secured to the primary rotary shaft, the planetary carrier and the main body portion won't make contact with one another in the axial direction, and thus friction loss won't occur between the planetary carrier and the main body portion in the axial direction. Therefore, in at least an embodiment of the present invention, friction loss in the planetary gear speed reduction device in the axial direction of the rotary shaft can be reduced.

To achieve the above, the planetary gear speed reduction device of at least an embodiment of the present invention comprises a magnetic sun gear, multiple magnetic planetary gears which revolve around the magnetic sun gear while rotating on the axes thereof, a magnetic internal gear which is arranged to surround multiple magnetic planetary gears from the outer circumferential side, multiple rotary shafts to which the multiple magnetic planetary gears are respectively secured, a planetary carrier which rotatably holds the multiple rotary shafts, and a main body portion which rotatably holds the planetary carrier and to which the magnetic internal gear is secured; the multiple rotary shafts are held by the planetary carrier such that the rotary shafts can move in the axial direction with respect to the planetary carrier; the planetary carrier is held by the main body portion such that the planetary carrier can move in the axial direction with respect to the main body portion; the total length of the gap in the axial direction between the planetary carrier and the main body portion on one end in the axial direction and the gap in the axial direction between the planetary carrier and the main body portion on the other end in the axial direction is smaller than the total length of the gap in the axial direction between the rotary shaft and the planetary carrier on one end in the axial direction and the gap in the axial direction between the rotary shaft and the planetary carrier on the other end in the axial direction; when the planetary carrier and the main body portion is in contact in the axial direction, a gap is to be created in the axial direction between the rotary shaft and the planetary carrier on both ends in the axial direction.

For example, in at least an embodiment of the present invention, the magnetic center of the magnetic sun gear and the magnetic internal gear in the axial direction coincides in the axial direction with the magnetic center of the magnetic planetary gear in the axial direction, and the external force in the axial direction exerted on the planetary carrier is larger than the magnetic attraction in the axial direction working between the magnetic sun gear, the magnetic internal gear and one magnetic planetary gear.

In the planetary gear speed reduction device of at least an embodiment of the present invention, the total length of the gap in the axial direction between the planetary carrier and the main body portion on one end in the axial direction and the gap in the axial direction between the planetary carrier and the main body portion on the other end in the axial direction is smaller than the total length of the gap in the axial direction between the rotary shafts and the planetary carrier on one end in the axial direction and the gap in the axial direction between the rotary shafts and the planetary carrier on the other end in the axial direction; when the planetary carrier and the main body portion are in contact in the axial direction, a gap is to be created between the rotary shafts and the planetary carrier on both ends in the axial direction. Therefore, in at least an embodiment of the present invention, if the magnetic center of the magnetic sun gear and the magnetic internal gear in the axial direction coincides in the axial direction with the magnetic center of the magnetic planetary gears in the axial direction, although friction loss in the axial direction may occur between the main body portion and the planetary carrier, no axial friction loss will occur between the multiple rotary shafts and the planetary carrier. Therefore, in at least an embodiment of the present invention, friction loss of the rotary shafts in the axial direction can be reduced.

In at least an embodiment of the present invention, the outside diameter of the magnetic sun gear and the outside diameter of the magnetic planetary gears may be equal. With this configuration, the magnetic planetary gears which are arranged next to each other on the outer circumferential side of the magnetic sun gear can be more distanced, preventing magnetic interference between the adjacently-arranged magnetic planetary gears. Therefore, the efficiency in transmitting the force between the magnetic sun gear and the magnetic planetary gears can be increased.

In at least an embodiment of the present invention, the planetary gear speed reduction device is equipped with a single magnetic sun gear and four magnetic planetary gears which are arranged at a pitch of 90° around the magnetic sun gear. In this case, the magnetic sun gear and the magnetic planetary gears may be formed in the same shape and that the number of magnetic poles of the outer circumferential surface of the magnetic sun gear and the number of magnetic poles of the outer circumferential surface of each of the magnetic planetary gears be equal. Also, in this case, the reduction rate of the planetary gear speed reduction device may be one-fourth. By configuring the device this way, the magnetic sun gear and the magnetic planetary gears can be in a common use; therefore, the number of different kinds of components used in the planetary gear speed reduction device can be reduced.

The planetary gear speed reduction device of at least an embodiment of the present invention can be used in a driving mechanism which is equipped with a motor, which is connected to the input side of the planetary gear speed reduction device and connected with the magnetic sun gear by the output shaft thereof. In this driving mechanism, friction loss can be reduced in the axial direction of the rotary shafts of the planetary gear speed reduction device. Also, in this driving mechanism, the output shaft of the motor is connected to the magnetic sun gear of the planetary gear speed reduction device, and the magnetic planetary gear speed reduction device is arranged at the position at which the rotation speed is relatively fast; therefore, the driving mechanism can be made quieter.

As described above, in the magnetic planetary gear speed reduction device of at least an embodiment of the present invention equipped with the magnetic sun gear and the magnetic planetary gears, the efficiency in transmitting the force between the magnetic sun gear and the magnetic planetary gears can be increased. Also, the driving mechanism can be made quieter in at least an embodiment of the present invention.

Also, in the magnetic planetary gear speed reduction device of at least an embodiment of the present invention equipped with the magnetic sun gear and the magnetic planetary gears, friction loss can be reduced in the axial direction of the rotary shafts to which the magnetic planetary gears are secured. Also, the driving mechanism in at least an embodiment of the present invention can be made quieter.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which:

<figref idref="DRAWINGS">FIG. 1</figref> is a side view of a driving unit which is equipped with a planetary gear speed reduction device of an embodiment of the present invention.

<figref idref="DRAWINGS">FIG. 2</figref> is a cross-sectional view of the planetary gear speed reduction device shown in <figref idref="DRAWINGS">FIG. 1</figref>.

<figref idref="DRAWINGS">FIG. 3</figref> is an exploded perspective view of a portion of the planetary gear speed reduction device shown in <figref idref="DRAWINGS">FIG. 2</figref>.

<figref idref="DRAWINGS">FIG. 4</figref> is a cross-sectional view of an E-E cross section of <figref idref="DRAWINGS">FIG. 2</figref>.

<figref idref="DRAWINGS">FIG. 5(A)</figref> is an enlarged view of an F section of <figref idref="DRAWINGS">FIG. 2</figref>; <figref idref="DRAWINGS">FIG. 5(B)</figref> is an enlarged view of a G section of <figref idref="DRAWINGS">FIG. 2</figref>.

<figref idref="DRAWINGS">FIGS. 6(A)-6(B)</figref> are diagrams to explain the configuration of the planetary gear speed reduction device of another embodiment of the present invention: <figref idref="DRAWINGS">FIG. 6(A)</figref> is an enlarged view of a portion corresponding to the F portion in <figref idref="DRAWINGS">FIG. 2</figref>; <figref idref="DRAWINGS">FIG. 6(B)</figref> is an enlarged view of a portion corresponding to the G portion in <figref idref="DRAWINGS">FIG. 2</figref>.

DETAILED DESCRIPTION

Embodiments of the present invention are described hereinafter referring to the drawings.

(Configuration of Driving Unit)

<figref idref="DRAWINGS">FIG. 1</figref> is a side view of a driving unit <b>2</b> which is equipped with a planetary gear speed reduction device <b>1</b> of an embodiment of the present invention. <figref idref="DRAWINGS">FIG. 2</figref> is a cross-sectional view of the planetary gear speed reduction device <b>1</b> shown in <figref idref="DRAWINGS">FIG. 1</figref>. <figref idref="DRAWINGS">FIG. 3</figref> is an exploded perspective view of a portion of the planetary gear speed reduction device <b>1</b> shown in <figref idref="DRAWINGS">FIG. 2</figref>. <figref idref="DRAWINGS">FIG. 4</figref> is a cross-sectional view of an E-E cross section in <figref idref="DRAWINGS">FIG. 2</figref>.

The planetary gear speed reduction device <b>1</b> (hereinafter denoted as “speed reduction device <b>1</b>”) configures a portion of a driving unit <b>2</b> which operates predetermined objects-to-be-operated (no illustration). The driving unit <b>2</b> is equipped with a motor <b>3</b> which is connected to the input side of the speed reduction device <b>1</b> and a speed reduction device <b>4</b> which is connected to the output side of the speed reduction device <b>1</b>. In this embodiment, a driving mechanism <b>5</b> is configured by the speed reduction device <b>1</b>, the motor <b>3</b> and the speed reduction device <b>4</b>. Also, the driving unit <b>2</b> is equipped with a screw member <b>6</b> connected to an output shaft of the speed reduction device <b>4</b>, a nut member <b>7</b> engaged with the screw member <b>6</b>, a sliding member <b>8</b> to which the nut member <b>7</b> and an object-to-be-operated are fixed, and a guide shaft <b>9</b> for guiding the sliding member <b>8</b>.

Note that in the description below, the Z<b>1</b> direction side in <figref idref="DRAWINGS">FIG. 1</figref>, etc. is the “front” side and the Z<b>2</b> direction side of <figref idref="DRAWINGS">FIG. 1</figref>, etc. is the “rear” side. In this embodiment, the motor <b>3</b>, the speed reduction device <b>1</b> and the speed reduction device <b>4</b> are arranged in this order from the rear side toward the front side. Also, the screw member <b>6</b>, the nut member <b>7</b>, the sliding member <b>8</b> and the guide shaft <b>9</b> are arranged on the front side of the speed reduction device <b>4</b>.

The speed reduction device <b>1</b> is a magnetic planetary gear speed reduction device and is equipped with a cylindrical magnetic sun gear <b>11</b> (hereinafter denoted as “sun gear <b>11</b>”) which is made from a permanent magnet, multiple cylindrical magnetic planetary gears <b>12</b> (hereinafter denoted as “planetary gears <b>12</b>”) which are made from permanent magnet, and a magnetic cylindrical internal gear <b>13</b> (hereinafter denoted as “internal gear <b>13</b>”) which is made from a permanent magnet. The speed reduction device <b>1</b> is also equipped with multiple rotary shafts <b>14</b> to which the multiple planetary gears <b>12</b> are respectively secured, a planetary carrier <b>15</b> which rotatably holds the multiple rotary shafts <b>14</b>, and a main body portion <b>16</b> which rotatably holds the planetary carrier <b>15</b> and to which the internal gear <b>13</b> is secured. The speed reduction device <b>1</b> of this embodiment is equipped with four planetary gears <b>12</b> and four rotary shafts <b>14</b>; the four rotary shafts <b>14</b> are rotatably held by the planetary carrier <b>15</b>.

The sun gear <b>11</b> is fixed to the outer circumferential surface of a cylindrical holding member <b>17</b>. The holding member <b>17</b> is arranged such that the axial direction of thereof coincides with the front-rear direction; the sun gear <b>11</b> is fixed to the holding member <b>17</b> while the front end side of the holding member <b>17</b> is inserted to the inner circumferential side of the sun gear <b>11</b>. To the holding member <b>17</b> an output shaft <b>3</b><i>a </i>of the motor <b>3</b> is fixed. More specifically described, the output shaft <b>3</b><i>a </i>is fixed to the inner circumferential surface of the holding member <b>17</b> while being inserted to the inner circumferential side of the holding member from the back. In other words, the output shaft <b>3</b><i>a </i>of the motor <b>3</b> is connected to the sun gear <b>11</b> via the holding member <b>17</b>.

The planetary gears <b>12</b> are secured to the outer circumferential surface of the rotary shafts <b>14</b>. More specifically described the planetary gears <b>12</b> are secured to the rotary shafts <b>14</b> while the rotary shafts <b>14</b> are inserted to the inner circumferential side of the planetary gears <b>12</b>. The rotary shafts <b>14</b> are arranged such that the axial direction thereof coincides with the front-rear direction. Each of the rotary shafts <b>14</b> is formed in a long and narrow cylindrical shape with a small step, in which the outside diameter of the front end portion and the rear end portion of the rotary shaft <b>14</b> is smaller than the outside diameter of the middle portion of the rotary shaft <b>14</b> in the front-rear direction. Thus, formed on the front end of the rotary shaft <b>14</b> is a step surface <b>14</b><i>a </i>facing toward the front, and formed on the rear end of the rotary shaft <b>4</b> is a step surface <b>14</b><i>b </i>facing toward the rear side. The step surface <b>14</b><i>a</i>, <b>14</b><i>b </i>is formed to be a plane orthogonal to the front-rear direction and to be annular.

As shown in <figref idref="DRAWINGS">FIG. 4</figref>, the four planetary gears <b>12</b> are arranged at a pitch of 90° around the sun gear <b>11</b>. Also, the four planetary gears <b>12</b> are arranged concentric to the sun gear <b>11</b>; an equal gap is created between the outer circumferential surface of the sun gear <b>11</b> and the outer circumferential surface of each of the four planetary gears <b>12</b>. The four planetary gears <b>12</b> are arranged at the same position in the front-rear direction; the magnetic centers of the four planetary gears <b>12</b> in the front-rear direction coincide with one another in the front-rear direction. The magnetic center of each of the planetary gears <b>12</b> in the front-rear direction is hereinafter denoted as the “magnetic center CL<b>1</b>”.

In this embodiment, the outside diameter of the sun gear <b>11</b> and the outside diameter of the planetary gears <b>12</b> are equal. In this embodiment, the sun gear <b>11</b> and the planetary gears <b>12</b> are formed in the same shape. In other words, the length of the sun gear <b>11</b> in the front-rear direction is equal to the length of the planetary gears <b>12</b> in the front-rear direction. The inside diameter of the sun gear <b>11</b> and the outside diameter of the planetary gears <b>12</b> are also equal; the outside diameter of the portion of the rotary shaft <b>14</b>, which is inserted to the inner circumferential side of the sun gear <b>11</b>, is equal to the outside diameter of the portion of the rotary shaft <b>14</b>, which is inserted to the inner circumferential side of the planetary gear <b>12</b>. Further, in this embodiment, the number of magnetic poles which are given on the outer circumferential surface of the sun gear <b>11</b> is equal to the number of magnetic poles given to the outer circumferential surface of each of the planetary gears <b>12</b>.

The internal gear <b>13</b> is arranged to surround the four planetary gears <b>12</b> from the outer circumferential side. The internal gear <b>13</b> is also arranged coaxially to the sun gear <b>11</b>, and a gap is created equally between the inner circumferential surface of the internal gear <b>13</b> and the outer circumferential surface of each of the four planetary gears <b>12</b>. The length of the internal gear <b>13</b> in the front-rear direction is equal to the length of the sun gear <b>11</b> in the front-rear direction. The sun gear <b>11</b> and the internal gear <b>13</b> are arranged in the same position in the front-rear direction. In this embodiment, also, the magnetic center of the sun gear <b>11</b> in the front-rear direction coincides in the front-rear direction with the magnetic center of the internal gear <b>13</b> in the front-rear direction. Hereinafter, the magnetic center of the sun gear <b>11</b> and the internal gear <b>13</b> in the front-rear direction is noted as “magnetic center CL<b>2</b>”.

As described above, the internal gear <b>13</b> is secured to the main body portion <b>16</b>. Therefore, as the sun gear <b>11</b> rotates, the four planetary gears <b>12</b> rotate with respect to the planetary carrier <b>15</b> and the planetary carrier <b>15</b> rotates with respect to the main body portion <b>16</b>. In other words, as the sun gear <b>11</b> rotates, the four planetary gears <b>12</b> revolve around the sun gear <b>11</b> while rotating on the axes thereof. In this embodiment, the number of magnetic poles given around the inner circumferential surface of the internal gear <b>13</b> is three times of the number of magnetic poles on the outer circumferential surface of the sun gear <b>11</b>. Therefore, in this embodiment, the reduction rate of the speed reduction device <b>1</b> is one-fourth.

The planetary carrier <b>15</b> holds the four rotary shafts <b>14</b> such that the four rotary shafts <b>14</b> can move in the front-rear direction with respect to the planetary carrier <b>15</b>. The planetary carrier <b>15</b> is equipped with a holding member <b>20</b> for holding the small diameter portions of the rotary shafts <b>14</b> on the front end, a holding member <b>21</b> for holding the small diameter portions of the rotary shafts <b>14</b> on the rear end, and an output shaft <b>22</b> secured to the holding member <b>20</b>. The holding member <b>20</b> is configured by a disc-like end plate portion <b>20</b><i>a </i>and four protruding portions <b>20</b><i>b </i>which protrude to the rear side from the end plate portion <b>20</b><i>a</i>. The holding member <b>21</b> is formed in a disc shape. The output shaft <b>22</b> is configured by a disc-like fixing portion <b>22</b><i>a </i>which is fixed to the holding member <b>20</b> and a shaft portion <b>22</b><i>b </i>which projects to the front side from the fixing portion <b>22</b><i>a. </i>

The end plate portion <b>20</b><i>a </i>is arranged such that the thickness direction thereof coincides with the front-rear direction. Formed in the end plate portion <b>20</b><i>a </i>are four through-holes <b>20</b><i>c</i>, through which the small diameter portions of the rotary shafts <b>14</b> on the front end are inserted, and a through-hole <b>20</b><i>d </i>into which the shaft portion <b>22</b><i>b </i>of the output shaft <b>20</b><i>a </i>is inserted. Also, in the center of the end plate portion <b>20</b><i>a</i>, a cylindrical protruding portion <b>20</b><i>e </i>protruding to the front is formed. The through-hole <b>20</b><i>d </i>is formed in the center of the end plate portion <b>20</b><i>a </i>and the inner circumferential surface of the protruding portion <b>20</b><i>e </i>is made as the through-hole <b>20</b><i>d. </i>

The four through-holes <b>20</b><i>c </i>are formed at a pitch of 90° with respect to the center of the end plate portion <b>20</b>. As shown in <figref idref="DRAWINGS">FIG. 4</figref>, the four protruding portions <b>20</b><i>b </i>are arranged at a pitch of 90° around the end plate portion <b>20</b><i>a</i>. Also, the protruding portions <b>20</b><i>b </i>are arranged so as to connect with the outer circumferential portion of the end plate portion <b>20</b><i>a</i>. The protruding portions <b>20</b><i>b </i>are arranged between the through-holes <b>20</b><i>c </i>in the circumferential direction of the end plate portion <b>20</b><i>a. </i>

The holding member <b>21</b> is arranged such that the thickness direction thereof coincides with the front-rear direction. The holding member <b>21</b> is fixed to the protruding portions <b>20</b><i>b </i>while making contact with the rear end surfaces of the protruding portions <b>20</b><i>b</i>. In the holding member <b>21</b>, the four through-holes <b>21</b><i>a</i>, through which the small diameter portions of the rotary shafts <b>14</b> on the rear end side are inserted, are formed. The four through-holes <b>21</b><i>a </i>are formed at a pitch of 90° around the holding member <b>21</b>. Also, in the center of the holding member <b>21</b>, a cylindrical protruding portion <b>21</b><i>c </i>protruding to the rear side is formed; the inner circumferential surface of the protruding portion <b>21</b><i>c </i>is made as the through-hole <b>21</b><i>b </i>passing through in the front-rear direction.

The output shaft <b>22</b> is fixed to the holding member <b>20</b> with the shaft portion <b>22</b><i>b </i>being inserted into the through-hole <b>20</b><i>d </i>from the rear side and with the front face of the fixing portion <b>22</b><i>a </i>being in contact with the back face of the end plate portion <b>20</b><i>a</i>. The front end potion of the shaft portion <b>22</b><i>b </i>protrudes to the front from the main body portion <b>16</b>. A gear <b>23</b> is secured on the front side of the shaft portion <b>22</b><i>b</i>. The gear <b>23</b> is a mechanical gear having multiple teeth around the outer circumferential surface thereof. More specifically, the gear <b>23</b> is a spur gear.

The main body portion <b>16</b> holds the planetary carrier <b>15</b> such that the planetary carrier <b>15</b> can move in the front-rear direction with respect to the main body portion <b>16</b>. The main body portion <b>16</b> is equipped with a main body frame <b>24</b> and bearings <b>29</b> and <b>30</b>. As shown in <figref idref="DRAWINGS">FIG. 2</figref>, the main body frame <b>24</b> is configured by a first frame [portion] <b>26</b> which configures the front end portion of the main body frame <b>24</b>, a second frame [portion] <b>27</b> which configures the rear end portion of the main body frame <b>24</b>, and a cover member <b>28</b> which connects the first frame [portion] <b>26</b> and the second frame [portion] <b>27</b>. In the center of the first frame [portion] <b>26</b>, a through-hole <b>26</b><i>a </i>passing through in the front-rear direction is formed. The bearing <b>29</b> is formed to be cylindrical, and the outer circumferential surface of the bearing <b>29</b> is secured to the through-hole <b>26</b><i>a</i>. On the inner circumferential side of the bearing <b>29</b>, a shaft portion <b>22</b><i>b </i>of the output shaft <b>22</b> is inserted; the shaft portion <b>22</b><i>b </i>is rotatably held by the bearing <b>29</b>.

In the center of the second frame [portion] <b>27</b>, a cylindrical protruding portion <b>27</b><i>a </i>protruding toward the front is formed. On the inner circumferential side of the protruding portion <b>27</b><i>a</i>, the rear end of the holding member <b>27</b> is positioned. The bearing <b>30</b> is formed to be cylindrical, and the inner circumferential surface of the bearing <b>30</b> is secured to the outer circumferential surface on the front end side of the protruding portion <b>27</b><i>a</i>. The bearing <b>30</b> is inserted through the through-hole <b>21</b><i>b </i>of the holding member <b>21</b>, and the holding member <b>21</b> is rotatably held by the bearing <b>30</b>. Formed on the front end of the protruding portion <b>27</b><i>a </i>is a contact surface <b>27</b><i>b </i>with which the rear end surface of the bearing <b>30</b> makes contact. The contact surface <b>27</b><i>b </i>is formed to be plane which intersect orthogonally with the front-rear direction and also formed to be annular. The outside diameter of the contact surface <b>27</b><i>b </i>is larger than the outside diameter of the bearing <b>30</b>, and the rear end surface of the protruding portion <b>21</b><i>c </i>of the holding member <b>21</b> can make contact with the contact surface <b>27</b><i>b. </i>

The cover member <b>28</b> is formed to be annular and fixed to the first frame [portion] <b>26</b> and the second frame [portion] <b>27</b>, covering the outer circumferential surface of the first frame [portion] <b>26</b> and the outer circumferential surface of the second frame [portion] <b>27</b>. The front end surface of the internal gear <b>13</b> is in contact with the rear end face of the first frame [portion] <b>26</b>, and the internal gear <b>13</b> is arranged on the inner circumferential side of the cover member <b>28</b>.

The speed reduction device <b>4</b> is equipped with a gear train (no illustration) including an input gear with which the gear <b>23</b> engages. Each gear that configures the gear train is a mechanical gear having multiple teeth around the outer circumferential surface thereof; the speed reduction device <b>4</b> is a mechanical reduction gear. More specifically, each gear configuring the gear train is a spur gear, and the speed reduction device <b>4</b> is a parallel axes reduction gear. Note that the speed reduction device <b>4</b> may be a planetary gear speed reduction device.

The screw member <b>6</b> is a trapezoidal screw thread, for example. A male thread is formed on the outer circumferential surface of the screw member <b>6</b>. The screw member <b>6</b> is arranged such that the axial direction thereof coincides with the front-rear direction. The screw member <b>6</b> is rotatably held by a frame of the driving unit <b>2</b>. To the rear end of the screw member <b>6</b>, a gear (no illustration) which engages with the output teeth of the speed reduction device <b>4</b> is secured. The nut member <b>7</b> is formed cylindrically; on the inner circumferential surface of the nut member <b>7</b>, a female thread which engages with the male thread of the screw member <b>6</b> is formed.

The guide shaft <b>9</b> is fixed to the frame of the driving unit <b>2</b> to be parallel to the screw member <b>6</b>. In other words, the guide shaft <b>9</b> is fixed to the fame of the driving unit <b>2</b> such that the axial direction thereof coincides with the front-rear direction. A through-hole into which the guide shaft <b>9</b> is inserted is formed in the sliding member <b>8</b>. As the screw member <b>6</b> turns, the sliding member <b>8</b> moves together with the nut member <b>7</b> along the guide shaft in a straight line in the front-rear direction. In other words, as the screw member <b>6</b> turns, an object-to-be-moved which is fixed to the sliding member <b>8</b> moves along the guide shaft <b>9</b> in a straight line in the front-rear direction.

(Positional Relationship in the Axial Direction Between Rotary Shafts and Planetary Carrier)

<figref idref="DRAWINGS">FIG. 5(A)</figref> is the enlarged view of the F portion of <figref idref="DRAWINGS">FIG. 2</figref>; <figref idref="DRAWINGS">FIG. 5(B)</figref> is the enlarged view of the G portion of <figref idref="DRAWINGS">FIG. 2</figref>.

In this embodiment, the external force exerted on the planetary carrier <b>15</b> in the front-rear direction is less than magnetic attraction in the front-rear direction working between the sun gear <b>11</b>, the internal gear <b>13</b> and one planetary gear <b>12</b>. In other words, the external force in the front-rear direction exerted on the planetary carrier <b>15</b> is less than the magnetic force in the front-rear direction working among the planetary gear <b>12</b>, which is secured to the primary rotary shaft <b>14</b>A which will be described later, the sun gear <b>11</b> and the internal gear <b>13</b>. Also, in this embodiment, as shown in <figref idref="DRAWINGS">FIG. 2</figref>, the magnetic center CL<b>1</b> of the planetary gears <b>12</b> coincides in the front-rear direction with the magnetic center CL<b>2</b> of the sun gear <b>11</b> and the internal gear <b>13</b>

Note that the gear <b>23</b> of this embodiment is a spur gear, for example; since almost no external force in the front-rear direction is exerted on the gear <b>23</b>, almost no external force in the front-rear direction exerts on the planetary carrier <b>15</b> if the driving unit <b>2</b> is installed such that the front-rear direction coincides with the horizontal direction. Even when the driving unit <b>2</b> is installed with the front-rear direction inclining to the horizontal direction, only the external force due to the gravity of the planetary carrier <b>15</b> and the gear <b>23</b> exerts on the planetary carrier <b>15</b> in the front-rear direction. Therefore, as described above, in this embodiment, the external force in the front-rear direction exerted on the planetary carrier <b>15</b> is less than the magnetic attraction in the front-rear direction working between the sun gear <b>11</b>, the internal gear <b>13</b> and one planetary gear <b>12</b>.

When one of the rotary shafts <b>14</b> is set as the primary rotary shaft <b>14</b>A and the remaining three rotary shafts <b>14</b> are respectively set as the secondary rotary shafts <b>14</b>B, the length of the large diameter portion from the step surface <b>14</b><i>a </i>to the step surface <b>14</b><i>b </i>of the primary rotary shaft <b>14</b>A is longer than the length of the large diameter portion from the step surface <b>14</b><i>a </i>to the step surface <b>14</b><i>b </i>of the secondary rotary shaft <b>14</b>B. In this embodiment, when a gap is created in the front-rear direction between the primary rotary shaft <b>14</b>A and the planetary carrier <b>15</b> on both ends in the front-rear direction, a gap C<b>1</b> between the step surface <b>14</b><i>a </i>of the primary rotary shaft <b>14</b>A and the rear surface of the end plate portion <b>20</b><i>a </i>in the front-rear direction is smaller than a gap C<b>2</b> between the step surface <b>14</b><i>a </i>of the secondary rotary shaft <b>14</b>B and the rear surface of the end plate portion <b>20</b><i>a </i>in the front-rear direction on the front side of the speed reduction device <b>1</b>, as shown in <figref idref="DRAWINGS">FIG. 5(A)</figref>; on the rear side of the speed reduction device <b>1</b>, as shown in <figref idref="DRAWINGS">FIG. 5(B)</figref>, a gap C<b>3</b> between the step surface <b>14</b><i>b </i>of the primary rotary shaft <b>14</b>A and the front surface of the holding member <b>21</b> in the front-rear direction is smaller than a gap C<b>4</b> between the step surface <b>14</b><i>b </i>of the secondary rotary shaft <b>14</b>B and the front surface of the holding member <b>21</b> in the front-rear direction.

In other words, in this embodiment, the total length of the gap C<b>1</b> in the front-rear direction between the primary rotary shaft <b>14</b>A and the planetary carrier <b>15</b> on the front side and the gap C<b>3</b> in the front-rear direction between the primary rotary shaft <b>14</b>A and the planetary carrier <b>15</b> on the rear side is smaller than the total length of the gap C<b>2</b> in the front-rear direction between the secondary rotary shaft <b>14</b>B and the planetary carrier <b>15</b> on the front side and the gap C<b>4</b> in the front-rear direction between the secondary rotary shaft <b>14</b>B and the planetary carrier <b>15</b> on the rear side.

Also, when a gap in the front-rear direction is created between the primary rotary shaft <b>14</b>A and the planetary carrier <b>15</b> on both ends in the front-rear direction, the gap C<b>1</b> is smaller than a gap C<b>5</b> created in the front-rear direction between the rear end surface of the protruding portion <b>21</b><i>c </i>and the contact surface <b>27</b><i>b </i>(see <figref idref="DRAWINGS">FIG. 5(B)</figref>), and the gap C<b>3</b> is smaller than a gap C<b>6</b> created in the front-rear direction between the front end surface of the protruding portion <b>20</b><i>e </i>and the rear end surface of the bearing <b>29</b> (see <figref idref="DRAWINGS">FIG. 5(A)</figref>). In other words, the total length of the gap C<b>1</b> in the front-rear direction between the primary rotary shaft <b>14</b>A and the planetary carrier <b>15</b> on the front side and the gap C<b>3</b> in the front-rear direction between the primary rotary shaft <b>14</b>A and the planetary carrier <b>15</b> on the rear side is smaller than the total length of the gap C<b>6</b> in the front-rear direction between the planetary carrier <b>15</b> and the main body portion <b>16</b> on the front side and the gap C<b>5</b> in the front-rear direction between the planetary carrier <b>15</b> and the main body portion <b>16</b> on the rear side.

For this reason, when the step surface <b>14</b><i>a </i>of the primary rotary shaft <b>14</b>A is in contact with the rear surface of the end plate portion <b>20</b><i>a</i>, or the step surface <b>14</b><i>b </i>of the primary rotary shaft <b>14</b>A is in contact with the front surface of the holding member <b>21</b>, a gap is created between the step surface <b>14</b><i>a </i>of the secondary rotary shafts <b>14</b>B and the rear end of the end plate portion <b>20</b><i>a</i>, a gap is created between the step surface <b>14</b><i>b </i>of the secondary rotary shafts <b>14</b>B and the front surface of the holding member <b>21</b>, a gap is created between the rear end surface of the protruding portion <b>21</b><i>c </i>and the contact surface <b>27</b><i>b</i>, and a gap is created between the front end surface of the protruding portion <b>20</b><i>e </i>and the rear end surface of the bearing <b>29</b>. In other words, when the primary rotary shaft <b>14</b>A and the planetary carrier <b>15</b> are in contact with each other in the front-rear direction, the gap is created between the secondary rotary shafts <b>14</b>B and the planetary carrier <b>15</b> and also between the planetary carrier <b>15</b> and the main body portion <b>16</b> on both ends of the speed reduction device <b>1</b> in the front-rear direction.

As described above, in this embodiment, the external force exerted on the planetary carrier <b>15</b> in the front-rear direction is less than the magnetic attraction in the front-rear direction working between the sun gear <b>11</b>, the internal gear <b>13</b> and the planetary gear <b>12</b> secured to the primary rotary shaft <b>14</b>A. Therefore, the planetary carrier <b>15</b> will never move further to the rear side from the state in which the step surface <b>14</b><i>a </i>of the primary rotary shaft <b>14</b>A and the rear surface of the end plate portion <b>20</b><i>a </i>are in contact. Also, the planetary carrier <b>15</b> will never move further to the front side from the state in which the step surface <b>14</b><i>b </i>of the first rotary shaft <b>14</b>A and the front surface of the holding member <b>21</b> are in contact. Therefore, the rear end surface of the protruding portion <b>21</b><i>c </i>and the contact surface <b>27</b><i>b </i>will not make contact with each other, and the front end surface of the protruding portion <b>20</b><i>e </i>and the rear end surface of the bearing <b>29</b> will not make contact with each other.

(Effects of This Embodiment)

As described above, the large diameter of the sun gear <b>11</b> and the large diameter of the planetary gear <b>12</b> are equal. Therefore, in this embodiment, it is possible to distance the adjacent planetary gears around the outer circumferential direction of the sun gear <b>11</b>, thus making is possible to prevent magnetic interference between the planetary gears <b>12</b> which are adjacently arranged in the circumferential direction. Therefore, in this embodiment, the efficiency in transmitting the force between the sun gear <b>11</b> and the planetary gears <b>12</b> can be increased.

In this embodiment, the sun gear <b>11</b> and the planetary gears <b>12</b> are formed in the same shape. Also, in this embodiment, the number of magnetic poles given around the outer circumferential surface of the sun gear <b>11</b> is equal to the number of magnetic pole given to the outer circumferential surface of each of the planetary gears <b>12</b>. Further, in this embodiment, the reduction rate of the speed reduction device <b>1</b> is one-fourth. For this reason, in this embodiment, the sun gear <b>11</b> and the planetary gears <b>12</b> can be in common use. Therefore, in this embodiment, the number of different kinds of components used to configure the speed reduction device <b>1</b> can be reduced. Also, in this embodiment, the output shaft <b>3</b><i>a </i>of the motor <b>3</b> is connected to the sun gear <b>11</b> and the speed reduction device <b>1</b> is arranged at a position at which the rotation speed is relatively fast; therefore, the driving unit <b>2</b> can be made quieter.

(Major Effects of This Embodiment)

As described above, a gap is created in the front-rear direction between the secondary rotary shafts <b>14</b>B and the planetary carrier <b>15</b> on both ends of the speed reduction device <b>1</b> in the front-rear direction when the primary rotary shaft <b>14</b>A and the planetary carrier <b>15</b> are in contact with each other in the front-rear direction. In this embodiment, the magnetic center CL<b>1</b> coincide in the front-rear direction with the magnetic center CL<b>2</b> of the sun gear <b>11</b> and the internal gear <b>13</b>. Therefore, according to this embodiment, even when friction loss in the front-rear direction occurs between one of the rotary shafts <b>14</b> (the primary rotary shaft <b>14</b>A, more specifically) and the planetary carrier <b>15</b>, no friction loss occurs between the remaining three secondary rotary shafts <b>14</b>B and the planetary carrier <b>15</b> in the front-rear direction. Therefore, according to this embodiment, friction loss of the speed reduction device <b>1</b> in the front-rear direction (that is, in the axial direction of the rotary shafts <b>14</b>) can be reduced.

Also, in this embodiment, the external force exerted on the planetary carrier <b>15</b> in the front-rear direction is less than the magnetic attraction in the front-rear direction working between the sun gear <b>11</b>, the internal gear <b>13</b> and the planetary gear <b>12</b> fixed to the primary rotary shaft <b>14</b>A; as described above, the rear end surface of the protruding portion <b>21</b><i>c </i>and the contact surface <b>27</b><i>b </i>will not make contact with each other and the front end surface of the protruding portion <b>20</b><i>e </i>and the bearing <b>29</b> will not make contact with each other. Therefore, in this embodiment, friction loss in the front-rear direction does not occur between the planetary carrier <b>15</b> and the main body portion <b>16</b>. Consequently, in this embodiment, friction loss in the front-rear direction in the speed reduction device <b>1</b> can be reduced.

In this embodiment, the outside diameter of the sun gear <b>11</b> and the outside diameter of the planetary gears <b>12</b> are equal. Therefore, in this embodiment, the adjacently-arranged planetary gears <b>12</b> around the outer circumferential direction of the sun gear <b>11</b> can be more distanced. Therefore, in this embodiment, the efficiency in transmitting the force between the sun gear <b>11</b> and the planetary gears <b>12</b> can be increased.

In this embodiment, the sun gear <b>11</b> and the planetary gears <b>12</b> are formed in the same shape. Also, in this embodiment, the number of magnetic poles given around the outer circumferential surface of the sun gear <b>11</b> is equal to the number of magnetic poles given around the outer circumferential surface of [each of] the planetary gears <b>12</b>. Further, the reduction rate of the speed reduction device <b>1</b> is one-fourth. Therefore, in this embodiment, the sun gear <b>11</b> and the planetary gear <b>12</b> can be in common use. Accordingly, the number of different kinds of components used to configure the speed reduction device <b>1</b> can be reduced. Also, in this embodiment, the output shaft <b>3</b><i>a </i>of the motor <b>3</b> is connected to the sun gear <b>11</b> and the speed reduction device <b>1</b> is arranged at a position at which the rotation speed is relatively fast; therefore, the driving unit <b>2</b> can be made quieter.

(Modification Examples of Planetary Gear Speed Reduction Device)

<figref idref="DRAWINGS">FIG. 6</figref> is a diagram to explain the configuration of the speed reduction device <b>1</b> of another embodiment of the present invention: (A) is an enlarged view of the portion of F in <figref idref="DRAWINGS">FIG. 2</figref>; (B) is an enlarged view of the portion of G in <figref idref="DRAWINGS">FIG. 2</figref>.

In the above-described embodiment, when the primary rotary shaft <b>14</b>A and the planetary carrier <b>15</b> are in contact with each other in the front-rear direction, a gap is created between the secondary rotary shafts <b>14</b>B and the planetary carrier <b>15</b> and between the planetary carrier <b>15</b> and the main body portion <b>16</b> in the front-rear direction. Beside this, when the planetary carrier <b>15</b> and the main body portion <b>16</b> are in contact with each other in the front-rear direction, a gap may be created between the four rotary shafts <b>14</b> and the planetary carrier <b>15</b> in the front-rear direction on both axial ends of the speed reduction device <b>1</b>.

In this case, for example, the lengths of the large diameter portions between the step surfaces <b>14</b><i>a </i>and the step surfaces <b>14</b><i>b </i>of the four rotary shafts <b>14</b> are all equal; the gap C<b>11</b> (see <figref idref="DRAWINGS">FIG. 6(A)</figref>) between the step surface <b>14</b><i>a </i>and the rear surface of the end plate portion <b>20</b><i>a </i>in the front-rear direction is the same among the four rotary shafts <b>14</b>, and the gap C<b>12</b> (<figref idref="DRAWINGS">FIG. 6(B)</figref>) between the step surface <b>14</b><i>b </i>and the front surface of the holding member <b>21</b> in the front-rear direction is also the same among the four rotary shafts <b>14</b>. Also, in this case, the gap C<b>13</b> (<figref idref="DRAWINGS">FIG. 6(B)</figref>) is created between the rear end surface of the protruding portion <b>21</b><i>c </i>and the contact surface <b>27</b><i>b </i>in the front-rear direction is smaller than the gap C<b>11</b>, and the gap C<b>14</b> (<figref idref="DRAWINGS">FIG. 6(A)</figref>) between the front end surface of the protruding portion <b>20</b><i>e </i>and the rear end surface of the bearing <b>29</b> in the front-rear direction is smaller than the gap C<b>12</b>.

In other words, the total length of the gap C<b>14</b>, created in the front-rear direction between the planetary carrier <b>15</b> and the main body portion <b>16</b> on the front side, and the gap C<b>13</b>, created in the front-rear direction between the planetary carrier <b>15</b> and the main body portion <b>16</b> on the rear side, is shorter than the total length of the gap C<b>11</b>, created in the front-rear direction between the rotary shafts <b>14</b> and the planetary carrier <b>15</b> on the front side, and the gap C<b>12</b>, created in the front-rear direction between the rotary shafts <b>14</b> and the planetary carrier <b>15</b> on the rear side. Also, in this case, even when the planetary carrier <b>15</b> moves in the front-rear direction, the planetary carrier <b>15</b> and the rotary shafts <b>14</b> will not make contact with each other; therefore, as shown in <figref idref="DRAWINGS">FIG. 2</figref>, the magnetic center CL<b>1</b> of the planetary gears <b>12</b> coincides in the front-rear direction with the magnetic center CL<b>2</b> of the sun gear <b>11</b> and the internal gear <b>13</b>.

In this case, friction loss occurs between the planetary carrier <b>15</b> and the main body portion <b>16</b> in the front-rear direction; however, no friction loss occurs in the front-rear direction between the four rotary shafts <b>14</b> and the planetary carrier <b>15</b>. Therefore, even in this case, friction loss in the speed reduction device <b>1</b> in the front-rear direction can be reduced. Note that the contact area between the planetary carrier <b>15</b> and the main body portion <b>16</b> in the front-rear direction is larger than the contact area between the primary rotary shaft <b>14</b>A and the planetary carrier <b>15</b> in the front-rear direction; therefore, the above-described embodiment can reduce friction loss in the speed reduction device <b>1</b> in the front-rear direction more effectively.

Note that, in the above-described embodiment, when the external force exerted on the planetary carrier <b>15</b> in the front-rear direction is larger than the magnetic attraction working between the sun gear <b>11</b>, the internal gear <b>13</b> and one planetary gear <b>12</b> in the front-rear direction, the planetary carrier <b>15</b> may move further to the back from the position in which the step surface <b>14</b><i>a </i>of the primary rotary shaft <b>14</b>A and the rear surface of the end plate portion <b>20</b><i>a </i>are in contact with each other or from the position in which the step surface <b>14</b><i>b </i>of the primary rotary shaft <b>14</b>A and the front surface of the holding member <b>21</b> are in contact with each other. Thus, in this case, the step surface <b>14</b><i>a </i>of the primary rotary shaft <b>14</b>A may make contact with the rear surface of the end plate portion <b>20</b><i>a </i>and the rear end surface of the protruding portion <b>21</b><i>c </i>may make contact with the contact surface <b>27</b><i>b</i>, and also the front end surface of the protruding portion <b>20</b><i>e </i>and the bearing <b>29</b> may make contact with each other. In other words, in this case, the primary rotary shaft <b>14</b>A and the planetary carrier <b>15</b> may make contact with each other in the front-rear direction, and the planetary carrier <b>15</b> and the main body portion <b>16</b> may make contact with each other.

On the other hand, even when the external force exerted on the planetary carrier <b>15</b> in the front-rear direction is larger than the magnetic attraction working between the sun gear <b>11</b>, the internal gear <b>13</b> and one planetary gear <b>12</b> in the front-rear direction, if a gap is created between the four rotary shafts <b>14</b> and the planetary carrier <b>15</b> in the front-rear direction on both axial ends of the speed reduction device <b>1</b> as in the modification example shown in <figref idref="DRAWINGS">FIG. 6</figref>, it is possible that the four rotary shafts <b>14</b> and the planetary carrier <b>15</b> will not make contact and friction loss in the speed reduction device <b>1</b> in the front-rear direction will be reduced. Therefore, when the external force exerted on the planetary carrier <b>15</b> in the front-rear direction is larger than the magnetic attraction working between the sun gear <b>11</b>, the internal gear <b>13</b> and one planetary gear <b>12</b> in the front-rear direction, a gap may be created between the four rotary shafts <b>14</b> and the planetary carrier <b>15</b> in the front-rear direction on both axial ends of the speed reduction device <b>1</b> when the planetary carrier <b>15</b> and the main body portion <b>16</b> are in contact with each other in the front-rear direction.

Note that if the external force exerted on the planetary carrier <b>15</b> in the front-rear direction is larger than the magnetic attraction in the front-rear direction exerted between the sun gear <b>11</b>, the internal gear <b>13</b> and one planetary gear <b>12</b>, a worm gear (a screw gear) or a bevel gear, in place of the gear <b>23</b>, is fixed on the front end of the shaft portion <b>22</b><i>b </i>when the gear <b>23</b> is a helical gear, or alternatively an impeller, in place of the gear <b>23</b>, is fixed on the front end of the shaft portion <b>22</b><i>b. </i>

(Other Embodiments)

The above-described embodiment is an example of an embodiment of the present invention; however, it is not limited to this, but can be varyingly modified within the scope of the present invention.

In the above-described embodiment, the speed reduction device <b>1</b> is equipped with four planetary gears <b>12</b>; however, the speed reduction device <b>1</b> may be equipped with any number of planetary gears other than four. Also, in the above-described embodiment, the sun gear <b>11</b> and the planetary gears <b>12</b> are formed in the same shape; however, as long as the outside diameter of the sun gear <b>11</b> and the outside diameter of the planetary gear <b>12</b> are the same, the shape of the sun gear <b>11</b> may be different from that of the planetary gear <b>12</b>.

In the above-described embodiment, the three secondary rotary shafts <b>14</b>B are formed in the same shape; however, one of the three secondary rotary shafts <b>14</b>B may be formed in a different shape from others. Also, in the above-described embodiment, the speed reduction device <b>1</b> is equipped with four planetary gears <b>12</b>; however, the speed reduction device <b>1</b> may be equipped with any number of planetary gears <b>12</b>. In other words, the speed reduction device <b>1</b> may be equipped with any number of rotary shafts <b>14</b>. Also, in the above-described embodiment, the sun gear <b>11</b> and the planetary gears <b>12</b> are formed in the same shape; however, the shape of the sun gear <b>11</b> may be different from that of the planetary gears <b>12</b>. For example, the outside diameter of the sun gear <b>11</b> may be different from the outside diameter of the planetary gears <b>12</b>.

In the above-described embodiment, the speed reduction device <b>4</b> is a mechanical speed reduction device; however, the speed reduction device <b>4</b> may be a magnetic speed reduction device. Also, in the above-described embodiment, the driving unit <b>2</b> is equipped with the speed reduction device <b>4</b>; however, the driving unit <b>2</b> may not be equipped with the speed reduction device <b>4</b>. In this case, the screw member <b>6</b> is connected to the output shaft of the speed reduction device <b>1</b>. Further, in the above-described embodiment, the driving unit <b>2</b> is equipped with one speed reduction device; however, the driving unit <b>2</b> may be equipped with two or more speed reduction devices <b>1</b>, which are connected in series. Also, in the above-described embodiment, the driving unit <b>2</b> moves an object-to-be-moved in a straight line; however, the driving unit <b>2</b> may rotate an object-to-be-moved.

While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention.

The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.